Vacuum induced healing of open wounds has recently been popularized by Kinetic Concepts, Inc. of San Antonio, Tex., by its commercially available V.A.C.® product line. The vacuum induced healing process has been described in commonly assigned U.S. Pat. No. 4,969,880 issued on Nov. 13, 1990 to Zamierowski, as well as its continuations and continuations in part, U.S. Pat. No. 5,100,396, issued on Mar. 31 1992, U.S. Pat. No. 5,261,893, issued Nov. 16, 1993, and U.S. Pat. No. 5,527,293, issued Jun. 18, 1996, the disclosures of which are incorporated herein by this reference. Further improvements and modifications of the vacuum induced healing process are also described in U.S. Pat. No. 6,071,267, issued on Jun. 6, 2000 to Zamierowski and U.S. Pat. Nos. 5,636,643 and 5,645,081 issued to Argenta et al. on Jun. 10, 1997 and Jul. 8, 1997 respectively, the disclosures of which are incorporated by reference as though fully set forth herein. Additional improvements have also been described in U.S. Pat. No. 6,142,982, issued on May 13, 1998 to Hunt, et al.
In practice, the application to a wound of negative gauge pressure, commercialized by Assignee or its parent under the designation “Vacuum Assisted Closure” (or “V.A.C.®”) therapy, typically involves the mechanical-like contraction of the wound with simultaneous removal of excess fluid. In this manner, V.A.C.® therapy augments the body's natural inflammatory process while alleviating many of the known intrinsic side effects, such as the production of edema caused by increased blood flow absent the necessary vascular structure for proper venous return. As a result, V.A.C.® therapy has been highly successful in the promotion of wound closure, healing many wounds previously thought largely untreatable.
The frequency at which negative pressure is applied to the wound, as well as the frequency of the pressure change over time, has a direct impact on the rate of wound healing. A variation of pressure change over time, not provided by current vacuum assisted therapy devices, is thought to significantly increase the rate of wound healing. Similarly, a rapid return to normal activities for the patient receiving wound therapy, may also improve the rate of wound healing, as increased physical activity is often accompanied by increased vascular circulation, which in turn leads to improved blood flow at the wound site. One barrier to a return to normal activities is limited battery life, which is a result of the electrical power required to power existing vacuum assisted wound therapy systems. Additionally, frequent inspection of the wound site is required in order to ensure the wound is not becoming infected. However, a rapid return to normal activities must not preclude the precautions that must be utilized during use of vacuum assisted therapy to prevent inadvertent spillage of wound exudates from the canister, or entry of wound exudates into the pumping mechanism.
Additional limitations are associated with the use of fixed frequency oscillating pumps in the prior art. Such limitations are the result of the size of the pump required to maintain the desired negative pressure at the wound site, and/or a reduction in battery life due to the power required to operate the oscillating pumps. Oscillating pumps, as known in the art, are typically designed for limited operating conditions. For example, to maximize low pressure flow rate at a fixed frequency. Typically the mass and/or stiffness of various components are altered to change the resonant frequency of the pump under the design operating conditions. If the pressure across the pump increases, the stiffness of the system is increased by back pressure across the diaphragm of the oscillating pump. The resonant frequency of the pump changes and the fixed frequency drive is not driving the pump at the optimum frequency. As a result, flow rate drops quickly and the capability of the pump to drive air at high pressure is limited. Accordingly, in order to provide increased flow rate at higher pressures requires either a sacrifice in flow rate at low pressures, or a pump of significantly greater size, when utilizing a fixed frequency oscillating pump.
For the foregoing reasons, there is a need for a vacuum assisted wound treatment system that is capable of automated pressure change over time. Additionally, there is a need for a more efficient vacuum assisted wound treatment system, that allows the patient more mobility, while reducing the risk of exudate spillage or pump contamination.
It is therefore an object of the present invention to provide a vacuum assisted wound treatment system that provides a means for increasing the stimulation of cellular growth by a variation of pressure over time.
A further object is to provide a system that is capable of extended operation in the absence of an alternating current power supply.
An additional object of the present invention is to provide a sanitary and cost effective means for sampling fluids drawn from the wound site without necessitating removal of the canister, or disturbing of the wound site.
Still another object of the present invention is to provide a vacuum assisted wound therapy device that can be secured to an object so as to reduce the likelihood of disturbance to the device, while still allowing convenient placement for its operation.